This invention relates to an emission abatement system and more particularly to NOx abatement using on board plasma-fuel-converter manufactured reducing gases in conjunction with an NOx absorber catalyst.
In order to reduce harmful emissions, internal combustion engines may be equipped with NOx absorber catalysts (also known as NOx traps or NOx absorbers) to reduce the amount of this harmful substance being released into the environment. There is a particularly pressing need for NOx and particulate control in diesel engines where pollution abatement is far less effective than in spark ignition engines.
The use of hydrogen gas as a reducing gas for NOx absorber catalyst regeneration has been taught by Boegner, et al., in U.S. Pat. No. 5,910,097 and by Guth, et al., in U.S. Pat. No. 5,599,758. However, a practical source of hydrogen that is well suited in this application was not identified. Sources other than a plasma fuel convertor can have disadvantages of relatively large size, inefficient use of fuel, slow response and difficulties in elimination of carbon formation from diesel and other fuels. Use of a plasma fuel converter removes these difficulties. A plasma fuel converter also has the advantages of robustness to sulfur and capability for varying the mix of hydrogen rich gas. The present application teaches how a plasma fuel converter can be employed in various combinations with SCR and NOx absorber catalysts. The plasma fuel converter is operated in such a way as to minimize cost and power losses.
U.S. patent application Ser. No. 09/182,537 filed Oct. 29, 1998, whose disclosure is incorporated herein by reference, disclosed utilizing the hydrogen rich gas from a plasma fuel converter to make a catalytic converter more active. That application also teaches that combustion of the hydrogen rich gas on catalytic surface increases the temperature of the catalyst and can be used for quick turn-on of the catalyst during cold startup. That patent application uses plasmatrons as the plasma fuel converter. U.S. Pat. Nos. 5,425,332; 5,437,250; and 5,887,554, whose teachings are incorporated herein by reference, describe plasmatrons suitable for use in the present invention.
In one aspect, the emission abatement system of the invention includes a source of emissions and an absorber catalyst or selective catalytic reduction (SCR) catalyst for receiving the emissions. A plasma fuel converter for generating a reducing gas from a fuel source is connected to deliver the reducing gas into contact with the absorber catalyst or SCR catalyst for regenerating the catalyst. In a preferred embodiment, the reducing gas is a hydrogen rich gas produced by a plasmatron which may be a partial oxidation plasmatron. The hydrogen-rich gas includes hydrogen and carbon monoxide. A catalyst may be disposed between the plasma fuel converter and the absorber catalyst to enhance the conversion to hydrogen rich gas. The source of emissions may be the exhaust from an internal combustion engine such as a diesel or a spark ignition engine or the exhaust from a turbine, boiler or burner in either a stationary or mobile configuration. In another embodiment, the system delivers at least a portion of effluent from the absorber catalyst to an input to the plasma fuel converter. In another embodiment, the system delivers at least a portion of effluent from the absorber catalyst to an input to the source of emissions such as a diesel engine. In another embodiment an oxidizing catalyst is positioned after the absorber catalyst or SCR catalyst in order to eliminate unreacted reducing components.
In yet another embodiment, a valve is provided for preventing the exhaust emissions from entering the absorber catalyst during absorber catalyst regeneration. A second absorber catalyst may be provided for receiving the emissions during regeneration of the first absorber catalyst. A second plasma fuel converter may be provided to deliver reducing gases to the second absorber catalyst. A portion of the hydrogen rich gas from the plasma fuel converter may be delivered to an input to the source of emissions which could be an internal combustion engine, turbine, boiler or burner. In a preferred embodiment, the absorber catalyst treats NOx emissions. The system of the invention may also treat particulates and CO emissions.